In an automatic door of a building or an electric slide door apparatus for a vehicle such as a wagon or a vain, an electric opening/closing apparatus is provided for sliding a door by a motor or the like to open/close the door. In the electric opening/closing apparatus like this, there is a possibility that an object is entrapped between a door frame and the door at the time of a closing operation of the door. An electric opening/closing apparatus including a control means for detecting an entrapment to stop the closing operation of the door or to reverse the closing operation to the opening operation of the door in such a situation is suggested.
In patent document 1 and patent document 2 mentioned below, an automatic opening/closing apparatus is described that can reliably detect an entrapment of an object by a moving body such as a door panel of a slide door apparatus of a vehicle. The automatic opening/closing apparatus described in these documents includes a pressure-sensitive sensor for detecting a pressing force generated by the entrapment of the object. Within the pressure-sensitive sensor, a long tube made of an elastic material, includes a cross hole in a casing portion of the tube. The cross hole is gradually displaced around a center of the tube. Wirings, which serve as electrodes, are helically provided in and along the cross hole so that each wiring is apart from other wiring. When the pressing force is applied to the pressure-sensitive sensor by the object being entrapped, the casing portion is elastically deformed, therefore the cross hole in the casing portion is deformed. At this point, the entrapment is detected by detecting that some of, or all of the wirings provided in the cross hole, are in contact with each other and are short-circuited.
However, for example, in a case where the pressure-sensitive sensor is provided along the door frame, there would be a possibility where bending of the sensor itself or a pressure applied to the pressure-sensitive sensor at the time of installation thereof should be taken into consideration and a degree of freedom of the installation is limited. Further, in the pressure-sensitive sensor, as described above, the wirings in the tube are made in contact one another by the pressing force generated by the entrapment of the object. Accordingly, though the pressure-sensitive sensor can preferably detect the entrapment if the object is firmly entrapped, the pressure-sensitive sensor cannot always preferably detect the entrapment at the stage that an object is in contact with the pressure-sensitive sensor immediately before the object is entrapped. Therefore, an entrapment sensor, which is more sensitive, is desired. For obtaining this, currently, as described in patent document 3 mentioned below, an entrapment sensor, which detects an entrapment on the basis of vibrations detected by a piezoelectric sensor, is being investigated and is gradually put to practical use.
Patent Document 1) JP3300660B2 paragraphs from 34 to 35, FIGS. 1 to 3)
Patent Document 2) JP3415014B2 (paragraphs 43 to 44, FIG. 8)
Patent Document 3) JP2003-106048A (paragraphs 5 to 7, 17 to 27, FIGS. 4 and 5)
However, it is not easy to directly change an entrapment sensor system, in which a conventionally utilized pressure-sensitive sensor is utilized, to an entrapment sensor system, in which a piezoelectric element is utilized.
A need thus exists for an entrapment detecting system, which can be obtained by changing a pressure-sensitive sensor utilized in an entrapment detection sensor to a piezoelectric sensor with a minimum system change, and which has good sensitivity. The present invention has been made in view of the above circumstances and provides such an entrapment detecting system.